From the prior art, products made out of composite material are widely known. Compared to injection molded parts comprising a relatively low amount of undirected fibers, laminated composites provide a superior performance and quality which mainly results out of a high concentration of oriented reinforcing fibres. Compared to products made by injection or by resin transfer molding technology, laminated products are more extensive in production, e.g., in the airplane or the race car industry, high quality light-weight and stiff parts made out of carbon, glass, or Kevlar fibres are used in areas where metals or other materials are not applicable. Especially for thin-walled structures laminated composites are often the preferred choice albeit they are difficult to make. Normal machining methods are in general not useable or only of limited utility in the production of laminated composite parts.
In general laminated composite parts are made in a labor intensive process in which at first directed carbon fibers are laid layer by layer into a cavity of a mold according to a predetermined layout plan. Afterwards the fibers are bonded together by a resin such that in the final product the fibers are surrounded by the resin and joined to each other. The embedded fibers are in general responsible for the stiffness and the loading capacity of the final product whereby the resin supports the fibers laterally. A further function of the resin is the protection of the fibers against external impacts.
Especially in mass production one of the biggest disadvantages of the nowadays commonly used processes consist in that the tool/press used for curing the laminate product is similarly to the tool used for preparing the layout of the fibers. Because it is to date not possible to move the non-finished laminate product from one tool to another one has therefore to wait until a curing process has come to an end and the equipment for curing becomes available for the next charge. An additional delay occurs due to the fact that nowadays, in general, it is necessary to adjust the temperature of the mold after one part has been made such that it becomes possible to lay the fibers out for the next part.
Today's production processes for composite materials which are based on autoclaves and prepreg press-technique often cause problems with respect to inclusion of air. In both processes, the production is based on tools with cavities which must be threatened with a form release agent such that the product is not bonded to the cavity. The form release agent causes a reduction of the surface energy and avoids sufficient wetting of the mould surface which leads to inclusion of air during the curing process of the resin. The inclusions are in the final part visible as pores or visible air bubbles which are well noticeable and affect the quality of the final product. In subsequent heat treatment, e.g. to increase the glass transition temperature (Tg), the inclusions of air may cause the surface to burst such that the final product is defective or additional treatment of the product is necessary to avoid additional pores affecting the quality. Beside potential influence on the load capacity, visible pores are in a high quality product not tolerable.
To obtain a high quality product, surfaces of laminated products must nowadays be coated by a clear coating which is very time and cost intensive. Normally the product is first coated by a clear coating or a primer which then needs to be dried. Subsequently it is necessary to grind and to subsequently clean the surface. Afterwards the exterior surface needs to be stopped/leveled out and dried again. Then an additional grinding and cleaning of the surface is in general necessary which then will be coated by a primer and the top coating. The repetition of the before mentioned steps may be necessary and depends mainly from the amount of pores present. By the today available production processes the formation of pores may not be prevent. As it becomes obvious the making of high quality laminated products is extremely time and cost consuming. Thereby the today available production processes are not applicable for the production of larger series of high quality laminated products.